1. Field of the Invention
The present invention relates to a method for manufacturing an anti-reflective coating. More particularly, the present invention relates to a method for controlling the properties of a dielectric anti-reflective coating (DARC) and manufacturing DARC.
2. Description of the Related Art
With the ever-decreasing size of feature line widths in semiconductor manufacturing, photolithographic process is carried out with increasing difficulties. As the line width is decreased, misalignment occurs with increasing frequency especially in the process of defining a conductive layer. Because the reflectivity index of the conductive layer is normally higher than the surrounding dielectric layer or insulation layer, light can easily reflect from the surface of the conductive layer during the definition of a photoresist pattern and lead to a change in dimension. Ultimately, the transferred pattern after the photolithographic process can be highly inaccurate. To prevent such dimensional deviation, an anti-reflective coating (ARC) is normally deposited over the conductive layer for reducing reflectivity.
Most anti-reflective coating can be classified into “bottom ARC” and “top ARC” according to whether the anti-reflective coating is formed over or under the photoresist layer. The anti-reflective coating can be fabricated using an organic material or an inorganic material. Typically, organic material layer such as polymer is deposited over the photoresist layer after it is formed. On the other hand, inorganic material such as titanium nitride (TiN), silicon dioxide (SiO2) or silicon oxynitride (SiON) is deposited over the conductive layer before forming the photoresist layer.
The anti-reflective coating is normally formed by carrying out a chemical vapor deposition process. For example, if the dielectric material constituting the anti-reflective coating is silicon dioxide, reactive gases such as silane (SiH4) and oxygen (O2) or tetra-ethyl-ortho-silicate (TEOS) can be employed. On the other hand, if the dielectric material constituting the anti-reflective coating is silicon oxynitride (SiOxNy), a plasma-enhanced chemical vapor deposition process is carried out using silane, nitrous oxide (N2O), ammonia (NH3) and nitrogen (N2) as the reactive gases.
However, if the step height of the device patterns on a semiconductor substrate is too large, the anti-reflective coating at different height levels will have a different reflectivity. In some cases, the difference in reflectivity may result in errors during the photolithographic process.